Holophane 420

This was a eBay find from a Canadian seller. It's in decent condition, however I want to clean up the corrosion inside and fill in some of the holes on the mounting plate that were drilled. I'm not entirely sure what the original mounting scheme was. The American ones had a hole intended for a 3/8" nipple but the Canadian ones don't have that. My hunch is that it was mounted to a bracket using the two upper side holes and the bottom centre hole. I saw one in the wild mounted using those holes.

Unfortunately the screws for the socket are rusted and stripped so I might have to resort to drilling them out.

I got the refractor off for cleaning already, I'm surprised it uses a sealed double refractor.